Classification of Ore Deposits | Economic Geology

Classification of Ore Deposits | Economic Geology

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  CLASSIFICATION OF OREDEPOSITS M.Hisan Mehdi Dr Abdul Shakoor Mastoi CLASSIFICATION OF ORE DEPOSITS Prepared by M.Hisan Mehdi 47/GLG/2K18 Submitted to Abdul Shakoor Mastoi CLASSIFICATION OF ORE DEPOSITS
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  CONTENT  Magmatic oredeposits. o Early magmatic deposits  Dissemination deposits  Segregation deposits o Late magmatic deposits  Sublimation ore deposits. o Hypothermal deposit o Mesothermal deposit o Epithermal deposit  Cavity Filling Deposits  Fissure vein  Shear zone deposits  Saddle reefs  Ladder Vein  Replacement Deposits  Pegmatitic ore deposits.  Contact metasomatic ore deposits.  Hydrothermal ore deposits  Cavity filling deposits.  Replacement deposits.  Sedimentation ore deposits.  Evaporation ore deposits.  Residual Deposits  mechanical concentration deposits o Eluvial placers o Stream Placers o Beach placers o Eolian placers o  Metamorphic ore deposits.
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  CLASSIFICATION OF OREDEPOSITS The Mixture of ore minerals are gangue minerals form an Ore deposit. The ore deposits are generally found enclosed within the country rocks. The ore deposits are formed in many different ways. Depending upon the process that may operate to produce them, the ore deposits may be classified as follow:  Magmatic ore deposits.  Sublimation ore deposits.  Pegmatitic ore deposits.  Contact metasomatic ore deposits.  Hydrothermal ore deposits  Cavity filling deposits.  Replacement deposits.  Sedimentation ore deposits.  Evaporation ore deposits.  Residual and mechanical concentration deposits  Metamorphic ore deposits. MAGMATIC ORE DEPOSITS: The magmatic ore deposits are the magmatic products which crystallize from magmas. The magmatic ore deposits are classified as follows: o Early magmatic deposits o Late magmatic deposits
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  Early magmatic deposits: Earlymagmatic deposits are formed during the early stage of the magmatic period. In this case the ore minerals crystallize earlier than the rock silicates. The Minerals of Nickel, Chromium, and Platinum are usually found as early magmatic deposits. The early magmatic deposits can be sub divided into two groups: o Dissemination deposits o Segregation deposits Dissemination deposits: When magma crystallizes conditions, a granular igneous rock is formed. In such a rock early formed crystals of may occur in dissemination. Segregation deposits: Magmatic segregation deposits are formed as a result of gravitative crystallization differentiation. In case, the ore mineral which crystallize early, get ocean-trated on a particular part of igneous part. The ore deposits thus formed are known as “Segregation deposits”. Early magmatic deposits are formed during the early stage of the magmatic period. In this case the ore minerals crystallize earlier than the rock Nickel, Chromium, and are usually found as early magmatic rly magmatic deposits can be sub Dissemination deposits Segregation deposits crystallizes under seated conditions, a granular igneous rock is formed. In such a rock early formed crystals of ore minerals Magmatic segregation deposits are formed as a result of gravitative crystallization differentiation. In such case, the ore mineral which crystallize trated on a particular part of igneous part. The ore deposits thus formed are known as “Segregation
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  Late Magmatic Deposits: Theore deposits which are formed to called late magmatic deposits. The late magmatic deposits contain those ore minerals which have crystallized at rather low temperature from the residual magma. The magma which is left after crystallization of early for is called residual magma. This magma frequently contains many ore minerals. The late magmatic deposits include most of the magmatic deposits of iron and titanium ores, these deposits are almost always associated with mafic igneous rocks. SUBLIMATION DEPOSITS: Sublimation is a very minor process of formation of ore deposits. Sublimation deposits contain only those minerals which have been volatilized by hear and subsequently redeposit in the same form at low temperature and pressure. The sublimation deposits are found associated with Volcanoes and Fumaroles. Sulfur of this origin has been mined in Japan, Italy, and Mexico. PEGMATITIC DEPOSITS: The late residual magma which is left in the last stage of crystallization, commonly contains silica, alkalis, water, carbon dioxide and concentration of rare elements and metals. Pegmatites are formed when this residual magma gets injected into the enclosing rocks. Many such pegmatite form valuable mineral deposits. The economic minerals which comm gemstone, and feldspar. Deposits are tantalum, niobium, tin, molybdenum and uranium are also found in some pegmatites. economic importance are mostly found associated with felsic igneous ro are quartz dioritic rocks. CONTACT METASOMATIC DEPOSITS: When certain igneous rocks invade carbonate rocks, such as limestone, ore deposits are formed near the contain by the reaction of the magmatic vapors on the host rock. These reactio place under condition of high temperature and pressure. The new minerals that develop may be composed of partly or wholly of constituents added from the magma. All the magma do not The ore deposits which are formed toward the close of magmatic period are called late magmatic deposits. The late magmatic deposits contain those ore minerals which have crystallized at rather low temperature from the residual magma. The magma which is left after crystallization of early formed rock silicates is called residual magma. This magma frequently contains many ore minerals. The late magmatic deposits include most of the magmatic deposits of iron and titanium ores, these deposits are almost always associated with mafic igneous Sublimation is a very minor process of formation of ore deposits. Sublimation deposits contain only those minerals which have been volatilized by hear and subsequently redeposit in the same form at low temperature and pressure. The sublimation deposits are found associated with Volcanoes and Fumaroles. Sulfur of this origin has been mined in Japan, Italy, and Mexico. The late residual magma which is left in the last stage of crystallization, commonly ilica, alkalis, water, carbon dioxide and concentration of rare elements formed when this residual magma gets injected into the enclosing rocks. Many such pegmatite form valuable mineral deposits. The economic minerals which commonly occur in pegmatite are mica, corundum, gemstone, and feldspar. Deposits are tantalum, niobium, tin, tungsten, molybdenum and uranium are also found in some pegmatites. Pegmatite`s economic importance are mostly found associated with felsic igneous ro CONTACT METASOMATIC DEPOSITS: When certain igneous rocks invade carbonate rocks, such as limestone, ore deposits are formed near the contain by the reaction of the magmatic vapors on the host rock. These reaction take place under condition of high temperature and pressure. The new minerals that develop may be composed of partly or wholly of constituents added from the magma. All the magma do not ward the close of magmatic period are called late magmatic deposits. The late magmatic deposits contain those ore minerals which have crystallized at rather low temperature from the residual med rock silicates is called residual magma. This magma frequently contains many ore minerals. The late magmatic deposits include most of the magmatic deposits of iron and titanium ores, these deposits are almost always associated with mafic igneous Sublimation is a very minor process of formation of ore deposits. Sublimation deposits contain only those minerals which have been volatilized by hear and subsequently redeposit in the same form at low temperature and pressure. The sublimation deposits are found associated with Volcanoes and Fumaroles. Sulfur The late residual magma which is left in the last stage of crystallization, commonly ilica, alkalis, water, carbon dioxide and concentration of rare elements formed when this residual magma gets injected into the enclosing rocks. Many such pegmatite form valuable mineral deposits. The only occur in pegmatite are mica, corundum, tungsten, Pegmatite`s economic importance are mostly found associated with felsic igneous rocks such
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  give rise tocontact metasomatic deposits. Mostly felsic intrusive of intermediate composition, such as monzonites and granodiorites yield Ore deposits. Contact metasomatic deposits usually carry ores of copper, iron, zinc and more rarely gold, silver and lead. The characteristic gangue minerals which are found associated with these ore deposits are high temperature silicates, such as garnet, diopside, tremolite, wollastonite, and phlogopite. The contact metasomatic deposits are generally discontinuous and irregular in shape. They are in general of comparatively small size. HYDROTHERMAL DEPOSITS: The epigenetic ore deposits formed by hydrothermal solution are called hydrothermal ore deposits. Hydrothermal Solution: The fluid left during the later stage of crystallization of intrusive magma when the main rock forming minerals have already been precipitated, is called “Residual fluid”. Metals originally present in the magma, concentrate in this fluid. This fluid which is a hot watery solution containing mineralized liquids derived from an intrusive magma is called “hydrothermal Solution” The hydrothermal solution move through cracks and opening present in the cracks and deposit their dissolved minerals there. Classification: On the basis of temperature of deposition, “Lindgren” has classified the hydrothermal deposits into three groups: o Hypothermal deposit o Mesothermal deposit o Epithermal deposit Hypothermal Deposit: These are the high temperature deposits which are formed closed to the intrusive body. Here the temperature ranges between 300° to 500 °C. The chief ore mineral which are commonly found in hypothermal deposits are arsenopyrite, wolframite, native gold and chalcopyrite
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  Mesotherma Deposits: These arethe intermediate temperature deposits which are formed at some distance outward from the intrusive igneous mass. Here temperature ranges between 200° to 300°C. The chief ore minerals of Mesothermal deposits are native gold, bornite, sphalerite galena and argentite. Epitharmal deposits: These are low temperature deposits formed very much away from intrusive body. Their temperature of formation ranges between 50° to 200° the commonly accor minerals are, Ruby, Silver, Stibnite and Cinnabar. On the basis of mode of formation, the hydrothermal deposits have been classified into two groups; o Cavity Filling Deposits o Replacement Deposits Cavity Filling Deposits: These deposits are formed when hydrothermal solution deposit their dissolve minerals in the various types of openings present in the rocks. Here precipitation of minerals is chiefly caused by change in temperature, pressure and chemical character of the mineralizing solutions. The characteristic features of cavity filling deposits are as follow: Crustification: The mineral which precipitates first lines the walls of the cavity. Its crystals grow inward and point toward the centre. Generally successive layers of different minerals are deposited upon the first one. This process is repeated until the filling is complete. A filling of this type is called crustification.
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  Comb Structure: If amineral vein prominent crystals projects inward from the walls. It is said to ha structure. Vugs: When a vein is not filled completely with the mineral matter open spaces are left in the centre. Such unfilled spaces are called vugus. Types of Cavity Filling Deposits: Depending upon the nature of opening the cavity filling opening deposits occur in a variety of shape and size. The common types of cavity filling deposits are: o Fissure vein o Shear zone deposits o Saddle reefs o Ladder Vein Fissure Vein: A fissure filled with ore is called fissure Vein. It is a tabular ore body which occupies one or more fissure within in a rock. Fissure vein deposits are the most important of all the cavity filling deposits. They are the chief source of most of the metals like gold, silver, copper, lead, zinc and mercury. Shear zone Deposits: The shear zones are the zone of thin and closely spaced and parallel fractures. Here as the opening are minute, the open space deposition is minor. However the large specific surface of the opening makes the Shear zones very susceptible to replacement. Hence many large and valuable ore deposits are foun If a mineral vein prominent crystals projects om the walls. It is said to have a comb lled completely with the mineral matter open spaces are left in the centre. Such unfilled spaces are called vugus. Types of Cavity Filling Deposits: Depending upon the nature of opening the cavity filling opening deposits occur in size. The common types of cavity filling deposits are: A fissure filled with ore is called fissure Vein. It is a tabular ore body which occupies one or rock. Fissure vein deposits are the most important of all the cavity filling deposits. They are the chief source of most of the metals like gold, silver, copper, The shear zones are the zone of thin and spaced and parallel fractures. Here as the opening are minute, the open space deposition is minor. However the large specific surface of the opening makes the Shear zones very susceptible to replacement. Hence many large and valuable ore deposits are found in the shear zones. Depending upon the nature of opening the cavity filling opening deposits occur in size. The common types of cavity filling deposits are:
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  Ladder Veins: Ladder veinsare commonly found in dykes they are the short, transverse, roughly parallel fracture that are filled with the ore. Because they appear like a ladder they are called ladder veins. REPLACEMENT DEPOSITS: Replacement is one of the important process in the formation of epigenetic mineral deposits. The chief epigenetic mineral deposits are contact metasomatic deposits, supergene mineral deposits and hydrothermal replacement deposits. The replacement deposits commonly contain ores of iron, lead, zinc, copper, silver and many non-metallic minerals the process of replacement may be summarized is follow: 1. Replacement is the chemical process of simultaneous capillary solution and deposition. process new minerals are substituted for earlier minerals and rocks. 2. placement occur through the action of hot vapours or hydrothermal solutions. The new minerals are carried in solution and the replaced substances are carried away in solution it is an open circuit not a closed one. 3. The replacement takes place molecule by molecule. consequently the shape, size, structure and texture of the rocks are faithfully preserved 4. post any Rock may be replaced by or but the rapidly soluble carbonate rocks are the most susceptible. certain structural features such as fissure may also localised replacement.
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  SEDIMANTATION DEPOSITS: Sedimentation depositsare the syngenetic ore deposits which are formed at the same time as the enclosing rock. They occur as beds in the sedimentary rocks. Some of the important sedimentation deposits are iron ore, manganese ore, copper ore, phosphates, limestone, Coal and clays these deposits are formed by the process of sedimentation. This process may be summarized as follows: 1. During weathering the materials are released from the source Rock. In this process the valuable mineral constituents are taken into solution the chief solvents are carbonated water organic acids and sulfate solutions. 2. Most of the valuable substances are transported either in suspension or in solution by means of river water to the sea. 3. In the sea, the valuable material is deposited mechanically, chemically or biochemical the chemical precipitation of materials in solution is controlled largely by the pH and Eh of the environment. The pH is responsible for the acidic are alkaline conditions and the Eh for the oxidation-reduction potential. Features of Sedimentation deposits: The sedimentation mineral deposits show many of the characteristics of normal sedimentary rocks. a. They commonly show bedding planes, ripple marks, and other sedimentary features. b. They normally occur as a bedded sedimentary rock interstratified c. They are often a deposit of great geographical Extent.
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  EVAPORATION DEPOSITS Many nonmetallic mineral deposits are formed as a result of evaporation of shallow and isolated bodies of saline water. the evaporation deposits are common salt gypsum and other salts of K, Mg. the process of evaporation may briefly be summarised as follows: 1) The main source of the evaporation deposits in a sea water. 2) -When a body of seawater is cut off during oscillations of land and sea its water evaporates. This leads to the concentration of soluble salts. 3) When supersaturation of a salt is reached that salt is precipitated and thus evaporation deposits are formed. 4) Evaporation deposits are mostly formed in warm climates where evaporation proceeds very rapidly RESIDUAL DEPOSITS: Residual deposits are formed a result of weathering of rocks in enclosed mineral deposits. the economic minerals which commonly occur is residual deposits iron, manganese, bauxite, tin, kyanite etc. During weathering the rock undergo chemical decay. in this process the undesirable constituents are removed in solution leaving behind a concentration of valuable minerals at the site of the original rock for necessary for the formation of residual mineral deposits are as follows. 1. The Rock undergoing weathering must contain some valuable minerals. 2. The valuable minerals must be resistant to chemical weathering. 3. The outcrop surface water cannot remove in soluble products of weathering. 4. There should be adequate when to carry away in solution the soluble products of weathering. Hence residual deposits commonly developed in tropical are subtropical climate. any non metallic mineral deposits are formed as a result of evaporation of shallow and isolated bodies of saline water. the chief minerals which occur is evaporation deposits are common salt gypsum and other salts of K, NA, CA, and g. the process of evaporation may briefly be summarised as follows: he main source of the evaporation eawater is cut off during oscillations of land and sea its water evaporates. This leads to the concentration of soluble salts. When supersaturation of a salt is reached that salt is precipitated and thus evaporation deposits are formed. its are mostly formed in warm climates where evaporation proceeds very rapidly. are formed a result of weathering of rocks in enclosed mineral deposits. the economic minerals which commonly occur is residual deposits iron, manganese, bauxite, tin, kyanite etc. undergo chemical decay. in this process the undesirable constituents are removed in solution leaving behind a concentration of valuable minerals at the site of the original rock for the stop the conditions necessary for the formation of residual mineral deposits are as follows. The Rock undergoing weathering must contain some valuable minerals. The valuable minerals must be resistant to chemical weathering. The outcrop surface should have low relief so that gravity and running water cannot remove in soluble products of weathering. There should be adequate when to carry away in solution the soluble products of weathering. Hence residual deposits commonly developed e subtropical climate. any non metallic mineral deposits are formed as a result of evaporation of chief minerals which occur is NA, CA, and its are mostly formed in warm climates where are formed a result of weathering of rocks in enclosed mineral deposits. the economic minerals which commonly occur is residual deposits are undergo chemical decay. in this process the undesirable constituents are removed in solution leaving behind a concentration the stop the conditions necessary for the formation of residual mineral deposits are as follows. The Rock undergoing weathering must contain some valuable minerals. The valuable minerals must be resistant to chemical weathering. should have low relief so that gravity and running There should be adequate when to carry away in solution the soluble products of weathering. Hence residual deposits commonly developed
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  MECHANICAL CONCENTRATION DEPOSITS: Thenatural separation of heavy minerals from light ones by means of moving water, or gravity is called "mechanical concentration" the mineral deposits formed by this process are called places. the minerals which commonly occur as placer deposits are diamond, gold, Platinum tinstone, magnetite, chromites, ilmenite and monazite. This process of mechanical concentration may be summarised as follows. This process of mechanical concentration may be summarised as follows. 1. The ore minerals are released from the rock by weathering and disintegration. 2. The disintegrated materials are carried downslope by water, air etc ultimately this material reaches the stream or seashore. 3. The moving water or air heavier placer minerals sink to bottom while the lighter material is carried further. Thus the heavier minerals are separated from the lighter ones. 4. In this way the heavy minerals Gate concentrated in the particular localities to form placer deposits. The condition necessary for the formation of placer deposits are: a) They must be primary source such as in ore deposit dissemination deposit or a low grade deposits which supplies or minerals. b) It must be exposed to weathering on slope from where the disintegrated material may be carried away by water, air, etc c) The ore minerals in the deposit must be of such chemical composition that it can be resist weathering.
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  Types of PlacerDeposits: 1) Eluvial placers 2) Stream Placers 3) Beach placers 4) Eolian placers Eluvial Placer: The eluvial placer deposits occur along the hill slopes here the mineral concentration is caused by gravity. When the debris is produced due to the weathering of rocks moves down slow, the heavier particles move more slowly than lighter ones. In this way heavy and minerals get concentrated to form in eluvial placer deposits. Stream Placer: These occur at various places along the stream. Here the mineral concentration is caused by running water. The weathered Rock material travel with stream water and the concentration of heavier minerals occurs in those places where the velocity of water slackens. Beach Placer: These deposits occur along sea shore. Where mineral concentration is caused by wave action. Eolian Placers: These occur in arid regions where mineral concentration is caused by wind action. Eolian processes are found in Australia.
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  METAMORPHIC DEPOSITS: Deposits formeddue to metamorphism may be divided into two groups: 1) Deposits formed due to metamorphism of pre-existing ore deposits 2) Deposits originated due to formation of new minerals during metamorphism of certain rocks. The End